Talking to People magazine, the former "Friends" star said, "I really admire David and his choice to take charge and better his life. I love and support him."
As for the reason behind Arquette's rehab check-in, sources tell that the actor is battling heavy drinking and bouts of depression.
With his breakup with Cox having made matters worse, an insider explained, "He's just not handling this situation well. He's really depressed."